Method of copperizing aluminum and aluminum alloys



United States Patent F METHOD OF COPPERIZIN G ALUMINUM AND ALUMINUMALLOYS Ledra M. Lawton and 'StuartT. Ross, Lockport, N. Y., assignors toGeneral Motors Corporation, Detroit, Mich., acorporation of Delaware NoDrawing. Application April 19, 1952, 'Serial No. 283,246

-Claims. (Cl. 117-130) This invention has to do with the application ofmetal coatings "to metal :surfaces and is more particularly concernedwith the application of a coating of copper to the surface of aluminumand aluminum alloys.

The usual methods for applying copper to aluminum and its alloys havenot been entirely satisfactory. For example, the usual methods ofelectroplating are'not satisfactory for coating aluminum withcopper andsatisfactory electroplatedcoatings can be produced only by means ofspecial and rather expensive methods. It also has been proposedheretofore to coatv aluminum with copper by contacting the aluminumsurface with fused cuprous chloride. However, 'thismethod has not provenentirely satisfactory in practice. It has also been desired to producealuminum havingclean coatings of copper thereon, such that the coatedmetals can :be soldered'more readily by ordinary methods 'thancanaluminum surfaces.

'One object of the present invention is to produce a novel and highlysatisfactory method for coating aluminum and its alloys with copper.

Another object is to treat aluminum and aluminum al- 'loy surfaces sothat they can be more readily soldered of an article or base member ofaluminum or an alu minum alloy composed preponderantly of aluminum maybe coated With an adherent, substantially impervious clean coppercoating by a process which includes first coating the article with aslurry consisting of cuprous chloride suspended in rosin which has been'plasticized with a terphenyl .type compound. The terphenyl type compondand rosin function to keep .the cuprouschloride in suspension. Afterthearticle has been coated with theslurry as just described, it istreatedto remove excess pl asticizer .to form a dry coating. After'thisis accomplished the aluminum article with-zthe :dry coating .is heatedto an elevated temperature for a short period of time sufiicient to.cause the copper tobe deposited on the aluminum surface in an adherentform.

In accordance with a preferred embodiment of the invention the slurryconsists .of .twop'arts by weight of finely .divided .cuprous chlorideand one part .by weight of a paste consisting of .finely powdered .rosinintimately mixed with :a terphenyl .type compound which :may beillustrated by .the .following .formula, CHsCeH4.'CsHs. Any one or moreof the isomers of terphenyl, singly or in mixtures, may be used.Specific examples are 1,3- diphenyl benzene and 1,4-diphenyl benzene.The preferred composition of the paste consists of 15 parts by weight offinely pulverized rosin and parts by weight of terphenyl as aplasticizer for the rosin. The rosin may be melted and the terphenyl.added. The aluminum or aluminum alloy article to be coated with copperhas 2,737,453 Patented Mar. 6, 1956 ice applied to the surface thereofat approximately room temperature .(abont Fli0 3R), a coating of 'theslurry prepared as just described. The coating then is dried as bynneans iQf iheating Ito vaporize and drive off excess plasticizer. About3010 :60 seconds at a temperature of approximately 3 0.01 to 350" F.i'has proven satisfactory in mostinstances. The .articlewith the driedcoating then is heated to a temperature :of 750 F. in an oxidizingatmosphere at atmospheric pressure for a short time thereby :producing:anadherent coating of copper on the article. time :of about .30 seconds-.or less is all that is necessary. .After the copper :coating is formedon the aluminumoraluminum alloy article the excess cuprous chloride androsin andplasticizer, if any, is washed olf the copper-coated article.An aqueous solution of potassium sc'hloride 101' ammonium hydroxide hasbeen found particularly "suitable :for ause in the washing operation.

While -.the ;-.foregoing;.-is';a specific example of apresentlyzpreferred mode :ofprocedure in accordance with the invention,considerable-variation :in the conditions may .be employed with success.:For example, the slurry of cuprous chloride and paste consisting ofrosin and terphenyltypecompondzmay waryirom about five parts by weightof :cuprous chloride-andone :part by .weight of the paste of rosin anditerphenyl to one part by weight of cuprous chloride and tone part byweight of the paste. Also, demperaturest'higher :and lower thanapproximately :room temperature may be employed in the first step ofcoating the aluminumor aluminumalloy with the slurry consisting .ofcuprouslclilon'de, pulverized rosin and the plasticizer. Temperaturesabove F. cause or tend to cause breaking .of 1hessuspension.Temperatures as low as!60 F. {oraevenrsomewhattlower than this may beemployed :under :certain .conditions. The temperature employed in the:drying step is :for thepurpose of driving 'ofi LthCJCXCCSS -plasticizer:and may be varied as desired withxthis purpose in mind.The'ftemperature of heating in forming "the copperrcoating may .alsovary considerably from 750 :Forexample, temperatures .up \to as high as850" F. :may be employed as well as lower tempera- ':tures such as';650F. :or even :as low as :600 F. under some conditions. Where the highertemperatures are employed it is unnecessary to .;use as long a time forthe heating .as where flower' temperatures are used. For .example, aslow as flotsecondsimay be used at a temperature-of 33b011t800 F. {Fortemperatures as 'low as 600 or.650 kit isgpreferred to employ longertimes "for'the heating .step.

Whileweryssatisfactory results .have been obtained by carrying out theheating step in an oxidizing atmosphere it is also contemplatedthatitheiheat:treatment may be carriedsout'in neutral iorrreducingatmospheres.

:In addition 'to;simpl.y'=iforming a coating of copper on aluminum theheat treatment at :elevated temperature conditions also causes somedifiusion of the copper into the aluminum so dhat theztreated articleconsists of alu- 'mi-num or an aluminumalloy ehaving'a diffused zone ofcopper-aluminum alloy and this is covered with a coatingofcopper-andin=case'the:article has been produced in an oxidizingatmosphere a *thin outer layer of an oxide of copper.

A'fter'theexcess cuprous chloride 'androsin (and plas-' ticizer if any)hasgbeen removed as "by washing, the aluminum "having the copper coatingthereon maybe soldered to other similarly coated articles or to othermetals. Also the copper coated article may be readily electroplated orcoated with another metal if desired.

Various changes and modifications of the specific embodiments of ourinvention described herein may be made by those skilled in the artwithout departing from the spirit and principles of the invention.

We claim:

1. A method of applying a copper coating to a base metal having asurface composed at least preponderantly of aluminum comprising coatingsaid base with a slurry of cuprous chloride suspended in rosinplasticized with a terphenyl type compound, thereafter heating said baseand slurry thereon for a time and at a temperature sufficient tovolatize excess plasticizer and thereby dry the slurry on said base andthen heating the base and dried coating at a higher temperature'than thedrying temperature and for a time sufficient to form a copper coating onsaid base.

2. A method of applying a copper coating to a metal base composed atleast preponderantly of aluminum comprising coating said base with aslurry of cuprous chloride suspended in rosin plasticized with aterphenyl type compound, said slurry being at a temperature within theapproximate range of 60 to 90 F., thereafter heating said base havingthe coating of the slurry thereon to a temperature and for a timesufiicient to drive off excess plasticizer to form a dry coating andthereafter heating the base metal and the dried coating thereon at atemperature within the approximate range of 600 to 850 F. for a timesuificient to form a copper coating on said base.

3. A method of applying a copper coating to a metal base composed atleast preponderantly of aluminum comprising coating said base with aslurry of cuprous chloride suspended in rosin plasticized with aterphenyl type compound, said slurry being at a temperature within theapproximate range of 60 to 90 F., thereafter heating said base havingthe coating of the slurry thereon to a temperature of about 300-350 F.for a time of about 3060 seconds to form a dry coating and thereafterheating the base metal and the dried coating thereon at a temperaturewithin the approximate range of 600 to 850 F. for a time of about 10 toabout 30 seconds.

4. A method of applying a copper coating to a base metal composed atleast preponderantly of aluminum comprising coating said base with aslurry of cuprous chloride suspended in rosin plasticized with terphenyl(CeH5-CsH4CsH5), the proportion of cuprous chloride in said slurryranging from about five parts by weight of cuprous chloride to about onepartby weight of the plasticized rosin to one part by Weight of cuprouschloride and one part by weight of plasticized rosin, thereafter dryingsaid coating by heating at a temperature on the order of 300 to 350 F.for about 30 to 60 seconds, thereafter heating the base metal and driedcoating to a temperature within the approximate range of 600 F. to 850F. for a period of not over about 30 seconds and thereafter removing anyexcess cuprous chloride and rosin.

5. A method of applying a copper coating to a base metal composed atleast preponderantly of aluminum comprising coating said base with aslurry of cuprous chloride suspended in rosin plasticized with terphenyl(CsHsCsH4CsH5), the proportion of cuprous chloride in said slurryranging from about five parts by weight of cuprous chloride to about onepart by weight of the plasticized rosin to one part by weight of cuprouschloride and one part by weight of plasticized rosin, said slurry beingat a temperature within the approximate range of 6090 F., thereafterdrying said coating by heating at a temperature on the order ofapproximately 300 to approximately 350 F. for about 30 to-60 seconds,thereafter heating the base metal and dried coat- 4 ing to a temperaturewithin the approximate range of 600 F. to 850 F. for a period of about10 to 30 seconds and thereafter removing excess cuprous chloride androsin.

6. A method of applying a copper coating to a base metal composed atleast preponderantly of aluminum comprising coating said base with aslurry consisting of about two parts by weight of cuprous chloride andone part by weight of a mixture of finely divided rosin and terphenyl(CsHsCsH4CeH5), said rosin and terphenyl being present in theproportions of about 15 parts by weight of rosin and 85 parts by weightof terphenyl, said slurry being at a temperature within the approximaterange of -90 F., then heating said base metal to a temperature ofapproximately 300 to 350 F. for a short period of time sufiicient toremove excess terphenyl and form a dry coating on said base, and thenheating said base metal with the dried coating thereon to a temperatureof approximately 750 F. for a time of approximately 10 to 30 seconds.

7. A method of applying a copper coating to a base metal composed atleast preponderantly of aluminum comprising coating said base with aslurry consisting of about two parts by weight of cuprous chloride andone part by weight of a mixture of finely dividedrosin and terphenyl(CsH5-C6H4CaI-I5), said rosin and terphenyl being present in theproportions of about 15 parts by weight of rosin and 85 parts by weightof terphenyl type compound, said slurry being at approximately roomtemperature, then heating said base metal to a temperature ofapproximately 300 to 350 F. for about 30 to 60 seconds to remove excessterphenyl and form a dry coat ing on said base and then heating saidbase metal with the dried coating thereon to a temperature ofapproximately 750 F. in an oxidizing atmosphere at atmospheric pressurefor a time of approximately 10 to 30 seconds.

8. A method of applying a copper coating to a base metal composed atleast preponderantly of aluminum comprising coating said base with aslurry consisting of two parts by weight of finely divided cuprouschloride and one part by weight of a paste consisting of about 85 partsterphenyl (C6H5-C6I'I4-C6H5) and '15 parts by weight of rosin, saidslurry being applied to the aluminum at a temperature of about F.,thereafter heating the coating for about 30 seconds to a temperature ofabout 350 F. to remove excess terphenyl and form a dry coating on saidbase and thereafter heating the base metal with the dried coating theronin an oxidizing atmosphere at a temperature of about 750 F. atatmospheric pressure for a time of about 30 seconds.

9. A process as in claim 4 in which any excess cuprous chloride androsin are removed by washing in an aqueous solution of the classconsisting of potassium chloride and ammonium hydroxide.

10. A process as in claim 8 in which any excess cuprous chloride androsin are removed by washing in an aqueous solution of the classconsisting of potassium chloride and ammonium hydroxide.

References Cited in the file of this patent UNITED STATES PATENTS675,584 Betts June 4, 1901 1,370,967 Hommel Mar. 8, 1921 2,331,356Swenson Oct. 12, 1943 2,462,631 Gittings et al. Feb. 22, 1949 2,551,712SOby May 8, 1951

1. A METHOD OF APPLYING A COPPER COATING TO A BASE METAL HAVING ASURFACE COMPOSED AT LEAST PREPONDERANTLY OF ALUMINUM COMPRISING COATINGSAID BASE WITH A SLURRY OF CUPROUS CHLORIDE SUSPENDED IN ROSINPLASTICIZED WITH A TERPHENYL TYPE COMPOUND, THEREAFTER HEATING SAID BASEAND SLURRY THEREON FOR A TIME AND AT A TEMPERATURE SUFFICIENT TOVOLATIZE EXCESS PLASTICIZER AND THEREBY DRY THE SLURRY ON SAID AND THENHEATING THE BASE AND DRIED COATING AT A HIGHER TEMPERATURE THAN THEDRYING TEMPERATURE AND FOR A TIME SUFFICIENT TO FORM A COPPER COATING ONSAID BASE.